1. Field of the Invention
This invention relates to preparing radioactive ion-exchange resins for disposal of their radioactively decaying atoms as waste. Decaying atoms attach to such resins by ion-exchange, for example, as nuclear power facilities clean the water which circulates inside the reactors. This specification teaches methods to reduce the volume of radioactive material which must be stored or buried after use of ion-exchange resins.
Exceeding results with present commercial practice in disposal of radioactive ion-exchange resins, this invention provides:
(i) removing water and its associated volume from the solid radioactive, ion-exchange resins, PA1 (ii) altering the chemical structure of the radioactive ion-exchange resins to remove ion-attractive groups, thereby avoiding further sorption of water, PA1 (iii) through the removal of the ion-attractive groups, also freeing the original radioactive ion-exchange resins from radioactive ions they had held, thereby forming simple polymer resin, PA1 (iv) depolymerizing simple polymer resin and vaporizing away nonradioactive vapors while retaining radioactive synthetic mineral, PA1 (v) operating in manner in which materials intended to be nonradioactive can be monitored for radioactivity prior to their release, and PA1 (vii) thus allowing safe release of material known to be nonradioactive, thereby reducing the volume of radioactive material that must be stored or buried. PA1 (i) Partial moisture removal and corollary separation of some nonradioactive water from even the solid radioactive ion-exchange resin normally can take place without difficulty. Squeezing, evacuation, and vaporizing are used commercially. PA1 (ii) Mixed hydroxides of sodium and potassium are often good material to add to firmly bind and hold decaying atoms which have attached to the ion-exchange resin. At 1/1 mol ratio and no excess water, these hydroxides fuse at 170.degree. C. If even small amounts water are present, these solutions form liquids at lower temperatures yet retain the ability to firmly bind the decaying atoms. The firmly bound decaying atoms will not escape from the hydroxide environment even if the organic material is chemically separated and removed from the decaying atoms. PA1 (iii) These same hydroxides, particularly if fused, can remove a cation-exchange sulfonyl reactive chemical group or similar group from a benzene ring and form a phenolic group which is neutralized by hydroxide. This replacement is important because it will allow later depolymerization and vaporization of decontaminated fragments of the substrate material of the radioactive ion-exchange resin. PA1 (iv) Heating the radioactive ion-exchange resin will partially depolymerize it. Partial liquefaction will occur both by the depolymerization and by melting of still polymerized segments of linear polymer. Normally the inventor has found it simple and effective to heat gently under air-free conditions which will allow the separational chemical reactions without oxidation. PA1 (v) Along with liquefaction the separational chemical reactions gradually shift to form different fragments as the polymer decomposition moves into the more heavily cross linked regions. As the resin decomposition proceeds, the temperature rises, the color of the decomposition products changes, and the residual solid polymer eventually becomes a charry residue. PA1 (vi) Also, as the ion-exchange resin breaks into the fragments, vaporization of the depolymerized material takes place. This vaporization is important and useful because it separates substantially nonradioactive material from the radioactive residue. PA1 (vii) Pyrolytic degradation breaks bonds in the cross-linked portion of the radioactive resin residue. Most of the degradation products from these separational chemical reactions are volatile at the temperatures used for depolymerization or the often higher temperatures used for pyrolysis. Vaporization is one of the better ways to separate volatile nonradioactive fragments formed here because the radioactive salts are effectively nonvolatile. Often it is useful to operate at less than atmospheric pressure. Other techniques again may be useful in assisting the vaporization, e.g., by steam distillation. PA1 as Taken from the Parent Application PA1 (1) One object of this invention is a method of preparing ion-exchange resin holding radioactive material including decaying atoms for its disposal comprising the steps below. PA1 (1a) At least part of the radioactive material is chemically attached to a bonding material such that decaying atoms become at least in part firmly bonded, whereby parent application first-treated resin residue is created. PA1 (1b) A chemical separation of at least part of the firmly bonded radioactivity from parent-application first-treated resin residue is effected, whereby parent-application second-treated resin residue at least partially freed of chemically attached decaying atoms is created. PA1 (1c) Depolymerizing, at least in part, the parent-application second-treated resin residue, whereby at least partially depolymerized parent-application resin residue is created. PA1 (1d) Bulk physical separation of at least part of the second-treated resin residue from the firmly bonded decaying atoms is effected, whereby substantially nonradioactive parent-application resin residue is created. PA1 (1e) In carrying out the steps above, at least one separation container Is used which will allow retention of at least part of one product resulting from the steps until it can be determined that unwanted release of decaying atoms will not occur as supposedly substantially nonradioactive resin residue is removed for nonradioactive disposal with corollary reduction in the space required for the radioactive disposal. PA1 (2) Another object of this invention is effecting one or more of the steps of the invention at least in part by heating. PA1 (3) Another object of this invention is effecting at least in part one or more steps of the invention in a separation container while the separation container is hermetically sealed. PA1 (4) Another object of this invention is effecting at least in part one or more steps of the invention in a separation container while the separation container is operating at other than atmospheric internal pressure. PA1 (5) Another object of this invention is effecting at least in part one or more steps of the invention at least in part in a separation container while the separation container is operating with an atmosphere in which the thermodynamic activity of oxygen is controlled. PA1 (6) Another object of this invention is pyrolyzing resin residue to break volatile organic fragments from the resin residue under reducing oxygen activity. PA1 (7) Another object of this invention is forming at least some carbon dioxide from substantially nonvolatile carbonaceous residue under oxidizing conditions. PA1 (8) Another object of this invention is using a catalyst in the decomposition of a resin residue. PA1 (9) Another object of this invention is forming and moving of at least one component of a resin residue as a vapor which condenses in substantially nonradioactive form. PA1 (10) Another object of this invention is using at least one type of material comprising metallic oxide to at least in part form said firmly bonded decaying atoms. PA1 (12) Another object of this invention is trapping potential air pollutants on substantially stable and nonvolatile salt. PA1 (13) Another object of this invention is specifically the binding into salt of chemical groups which would complicate later disposal of substantially nonradioactive resin residue by incineration. PA1 (14) Another object of this invention is chemically altering ion-exchange resin holding radioactive material to render it substantially incapable of holding moisture. PA1 (15) Another object of this invention is the use of solvent extraction to separate nonradioactive material from radioactive material by chemical alteration of the original ion-exchange material holding decaying atoms. PA1 (16) A further object of this invention is to monitor a separated phase while it is still in containment in order to assure it is substantially nonradioactive. PA1 (17) A further object of this invention is to use a technique to assist transport of organic vapor to a condensation region of a separation container.
This invention is urgently needed:
First, most commercial nuclear power plants in the United States have already lost all access to any burial for their radioactive wastes--such wastes must be stored. Also, most other commercial operations which generate radioactive waste are faced with an uncertain period of storage as their wastes accumulate. Without storage space most of the commercial operations indicated would have to close down. (Later note: The Barnwell burial site reopened Jul. 1, 1995.)
Long-term radioactive storage of radioactive wastes was being planned, for example, at the Perry nuclear power facility near Cleveland in October, 1992.
Both State and Federal new burial facilities were supposed to be prepared: Federal law once mandated that states would have to supply radioactive burial sites, but the requirement was overturned by the U.S. Supreme Court; litigation continues. The Federal burial site for commercial radioactive waste was supposed to be available in 1998, but estimates say it is 15 years behind schedule.
Second, open Federal sites for burial of radioactive wastes are rapidly filling while waste generation continues, and there are strong objections by U.S. citizens to any burial or transportation of radioactive materials.
Third, environmental logic requires that radioactive burial volumes be minimized. Lacking the teaching of this invention, current Federal practice is to bury considerably more waste than would be buried with improved practice as described in this invention. For those organizations which must store their radioactive wastes, excessive storage is illogical both environmentally and economically.
2. Description of the Related Art
As noted above, decaying atoms in water are often removed onto ion-exchange resin. In much industrial practice, and presumably also widely at Federal facilities, the radioactive ion-exchange resin is packaged wet in drums for storage or disposal. Because steel drums rust, concrete reinforcement was added for some physical protection against radioactive leakage.
Current practice often uses glass-reinforced plastic drums with no interior reinforcement against their damage. Other than to remove some of the water, the resin characteristics are not changed before storage or burial. Such resin, if exposed to weathering, can release radioactive atoms it holds.
Long-Term Burial: As noted above, long-term burial as used in most past practice is not now an option for most commercial generators of radioactive waste. Federal burial grounds are filling up, and Federal generators of nuclear waste are facing many future problems with burial, particularly excessive burial. Waste-volume reduction is needed.
Burial has always been considered a problem. In the inventor's experience from 1946 and still continuing, there has been concern that much buried radioactive material would have to be dug up and moved. Times and environmental concerns, as well as standards for acceptable burial, have changed, both as to form and volume of materials which are acceptable.
Ion-exchange resins have long been considered a special problem because they can pick up and hold large volumes of water of hydration, swelling in the process.
Open-Flow Incineration: The term open-flow incineration is used here for typical incineration such as is used in incinerating either garbage or wastes of paper and plastic. Here oxygen, usually in air mixed with other gases, flows over hot material and reduces the material substantially to ash. Typically, water vapor and carbon dioxide are the principal gases formed. Other gases, e.g., noxious oxides of nitrogen and of sulfur, may form. Bits of the ash dust typically will be carried along with the flowing gas.
Traps to remove the gaseous oxides, plus filters to remove the dust, can be installed along the flowing-gas path to the stack. Most of the time these traps work well, e.g., when such systems are used to burn mildly radioactive paper and rubber gloves, which generate ash.
Open-flow incineration systems neither (i) hold the gas for precise analysis for carried radioactivity before the gas is released to the atmosphere nor (ii) stop the incineration instantaneously if excessive radioactivity is detected in material escaping up the stack. One learns too late that something has gone wrong and uncontrolled decaying atoms are escaping.
A large incinerator at is planned Oak Ridge, Tenn., for commercial nuclear waste. Discussions by the inventor with incinerator personnel suggest that the facility will not be suitable for ion-exchange resin for reasons discussed below.
Incineration of Radioactive Ion-Exchange Resin: In addition to the incineration problems noted, radioactive ion-exchange resin lacks ash-forming materials to trap the radioactive dust released as incineration occurs. This dust, if not trapped, may be expected to be blown around by the gas stream.
Also, a significant fraction of the resin volume is as inorganic chemical groups which were put there to trap ions. Incineration releases chemically nonradioactive but noxious gases which must be trapped for environmental reasons.
Trapping the noxious gases and the radioactive dust by conventional technology, even if the technology were to work perfectly, might actually increase the volume of radioactive waste to be stored or buried.
For these and other reasons, burial is widely preferred over open-flow incineration for disposal of radioactive ion-exchange resins--incineration often is not a good choice.
Because a dictionary definition of incineration involves "reducing something to ash," it is noted that incineration, as used in this disclosure, includes oxidation of carbonaceous residues in the vicinity of radioactive oxides or other salts to remove the carbon as carbon dioxide.
The treatment of this invention is not an open-flow system--rather, all gases are trapped and held available for radioactive monitoring before they are released.
Pyrolysis of Radioactive Ion-Exchange Resin: It is noted that pyrolysis is often combined inherently with incineration because of normal lack of local oxygen at heated combustion regions.
Such normal pyrolysis fails to utilize the concept of depolymerization, followed by pyrolysis, if that is required, as offered by the present invention. With more control of the chemical bond breakage, one can (i) depolymerize ion-exchange resin, (ii) meanwhile break off large organic fragments from the depolymerizing resin, (iii) thereby vaporizing mostly condensible vapors, and (iv) condense these vapors and monitor the condensate for radioactivity.
Over 95% reductions in the volumes of potentially radioactive gases generated may be achieved with the present invention, as compared with use of normal incineration practices.
Aqueous Oxidation: Processes are being developed that employ hydrogen peroxide to oxidize ion-exchange resin to carbon dioxide, water, and derivatives of sulfonyl and trimethyl amine groups.
As compared with the present invention, aqueous oxidation, like open flow incineration, generates very large volumes of potentially radioactive gas. With aqueous oxidation, the gas is generated in radioactive water which may become entrained in continuous gas flow. Such flow may lead to very finely divided, highly radioactive particles that, when dry, can be carried in even gentle winds.
Also, the system must be treated to handle sulfates and radioactive materials after the ion-exchange resin has been destroyed. The peroxide may also convert radioactive cations to anions, which may be harder to collect and dispose of than were the original anions.
With the present invention, in contrast, sulfates formed from the cation-exchange resin may become part of synthetic minerals, and anions present may become cations that coprecipitate readily inside the synthetic minerals. Such minerals have much better anticipated lives for protecting against release of decaying atoms than do steel, concrete, or plastic, as now used.
Other Methods of Decontamination from Decaying Atoms: Numerous other decontamination methods might remove and isolate decaying atoms from a source, e.g., coprecipitation alone, solvent extraction, vaporization, and leaching.
For solid radioactive material such as an ion-exchange resin, however, most of these techniques are substantially inoperable because the nonfluidity of the solid effectively blocks thorough removal of the decaying atoms in the interiors of solids.
Many customary techniques for handling solids such as metals or oxides use aqueous solutions to dissolve them. Such solutions can then be subjected to near-equilibrium separations processes. However, unless there is resin destruction, aqueous dissolutions are largely inoperable for solid radioactive ion-exchange resins.
Summary Regarding Related Art: The existing art for storage or burial of radioactive ion-exchange resins involves excessive volumes which are environmentally and economically unsatisfactory.
Likewise, the concepts of existing art for resin destruction appear to be environmentally and economically less satisfactory than are the concepts of the present invention.
Patents Noted:
Buchwalder, et al., U.S. Pat. No. 4,122,048, used a basic compound to block the active sites of certain contaminated ion-exchange resins so that these resins could be encapsulated in further resin for disposal. The procedure neither offers long-term environmental protection nor reduces the radioactive volume to be disposed of.
Laske, et al., U.S. Pat. No. 4,732,705, added various chemicals to reduce the swelling upon wetting of ion-exchange resins. This treatment may reduce the disposal volume of the resins, but it does not offer long-term environmental protection and may actually tend to release the radioactive ions the resin initially held.
Knotic, et al., U.S. Pat. No. 4,235,738, added high-boiling oil to ion-exchange resin prior to its heating to produce decomposition of the resin by carbonization. This treatment may assist in retaining the decaying atoms, especially by lowering the carbonization temperature, and avoiding some vaporization of decaying atoms. However, the carbonaceous material formed (i) fails to offer long-term environmental protection of the entrapped decaying atoms, and (ii) the carbon present during carbonization tends to increase the decomposition and vaporization of materials such as radioactive cesium oxide.
Kawamura, et al., U.S. Pat. Nos. 4,636,335 and 4,654,172, use low temperature pyrolysis to separate ion-exchange groups from ion-exchange resins prior to high temperature pyrolysis. Then the hot resin residues are compressed into a "molded article". They note, "In this way, decomposition gases generated during thermal decomposition are separated in two stages and gaseous nitrogen oxides (NO.sub.x) and gaseous sulfur oxides (SO.sub.x) which require careful exhaust gas disposal treatment are generated only in the first stage thermal decomposition . . . " ('335, column 2).
This Kawamura, et al., preliminary procedure reduces the volume of gas initially produced and yields a carbonaceous residue that provides largely physical, rather than chemical, trapping of the decaying atoms. However, the '172 claims 7-9 also note "presence of a vitrifying agent which absorbs volatile radioactive substances" that were "added before the pyrolysis at a low temperature" such as glass frit. A frit has substantially no contact with most of the decaying atoms, and it therefore cannot pick them up.
The '335 and '172 treatments (i) do not chemically anchor the decaying atoms in a condensed phase, i.e., as solid or liquid, prior to vaporizing resin components, (ii) do not afford dependable environmental protection against release of many radioactive elements if the hydrocarbons of the carbonaceous residue have become oxidized by air or otherwise, and (iii) do prevent precise reversal of the polymerization reactions which originally formed the ion-exchange resin.